The US State Department on Tuesday said it has seen reports of a "marked and troubling increase" in civilian deaths following the start of Russia’s air campaign in support of Bashar al Assad's regime in the country.
Department spokesman Mark Toner mentioned the deaths of hundreds of civilians recently reported by non-governmental organisations and called them “extremely disturbing."
"We've seen a marked and troubling increase in reports of these civilian casualties since Russia commenced its air campaign there," Toner said.
Toner noted that the high civilian death toll is a concern US Secretary of State John Kerry has raised with Russia.
The Syrian Network for Human Rights published a report on Monday saying Russian air strikes have killed 849 civiians including more than 100 children.
A recent Amnesty International report says air strikes conducted by Russia in support of Bashar al-Assad's regime in Syria have resulted in hundreds of civilian deaths and damaged hospitals and homes.
According to the report, following "remote investigations" of 25 attacks between Sept. 30 and Nov. 29 , Russia - which claims its armed forces are only striking terrorist targets - seriously failed in "respect[ing] international humanitarian law" by causing at least 200 civilian casualties.
The report says there is evidence showing that Russia "has unlawfully used unguided bombs in densely populated areas," such as on residential areas, homes, a mosque and a busy market, as well as medical facilities.
Russia rejected the report, accusing it of containing "trite cliches." Russian Defence Ministry spokesman Igor Konashenkov said it was based on "fake information."
The criticism came as Syrian opposition groups and regime representatives are expected to start talks aimed at solving the conflict.
The US is urging Russia, which has been one of the main allies of the Assad regime since the civil war started almost five years ago, to help facilitate negotiations between the regime and the rebels.
UN estimates suggest that at least 250,000 people have been killed since the war in Syria began in March 2011, and that half of the country’s population has been displaced both internally and externally.